RU2331949C1 - Method of roduction structure "silicon-on-insulator" - Google Patents

Abstract

FIELD: processes.

SUBSTANCE: invention can be used for micro- and nanoelectronics for manufacturing radiation-hardened integrated chips, sensors and electromechanical system compositions on insulating base. Concept of the invention: as received structure "silicon-on-insulator" plate of single-crystalline silicon of p-type conductivity is put to the anodic etching in electrolytic solution, which contents hydrogen and fluorine ions, and to the anodic oxidation in water solution of electrolytes. After every of procedures plate is dried in inert atmosphere at temperature in the range from 180°C till 400°C. Before high-temperature annealing in temperature range from 1300°C till 1370°C silicon plate with porous layer is encapsulated by protective film. Defects of "silicon tubes" type of buried insulating layer are remedied.

EFFECT: process of production is simplified and operating costs are decreased.

9 cl, 3 dwg

Description

The invention relates to the field of electronic technology, mainly micro- and nanoelectronics, and can be used in the manufacture of radiation-resistant integrated circuits, sensors and devices of microelectromechanical systems on insulating substrates.

A known method of producing structures "silicon-on-insulator" (US patent No. 3622382, IPC B44d 1/18, 1971), including implantation of large doses of oxygen sufficient to form an insulating layer of silicon dioxide in the region of penetration of ions, and subsequent high-temperature annealing at temperatures 1100-1200 ° C.

The main disadvantages of this method are the presence of a large number of dislocations in the silicon working layer caused by high mechanical stresses arising during the implantation process, and the formation of an intermediate region enriched in silicon oxide precipitates at the interface between the silicon working layer and the insulating layer. It is also a disadvantage of the known method and the fact that this method uses an ion implantation operation performed using an accelerator designed to irradiate materials with oxygen ions at high current densities. Such an accelerator is a complex specialized equipment that requires highly qualified service during operation.

Of the known methods for obtaining the structure of "silicon-on-insulator" closest to the claimed is the method presented in US patent No. 4676841, George C. Celler, IPC H01L 21/265 1987. According to this method, this structure is obtained by implanting large doses of oxygen into a silicon wafer heated to 500 ° C, encapsulating a silicon dioxide protective film, and then annealing it at high temperature. The dose of implantation is 1.8 x 10 ¹⁸ at the oxygen / cm ^2. Annealing is carried out at temperatures of 1300-1400 ° C.

The main disadvantage of this method is the fact that the method uses an ion implantation operation carried out using a specialized accelerator designed to irradiate silicon wafers placed in a special receiving chamber with oxygen ions at high current densities and elevated temperatures. Accelerators of this class are the most sophisticated technological equipment requiring highly qualified service and are not used in the manufacture of electronic equipment on silicon lines, universally equipped with conventional accelerators, mainly intended for doping semiconductor materials. On the basis of such accelerators, a separate, expensive production of silicon-on-insulator structures is being created. Also a disadvantage of this method of obtaining structures is the appearance of defects of the "silicon tube" type in a buried insulating layer, arising as a result of masking the irradiated surface with microparticles adsorbed on the surface of the silicon wafer during implantation and preventing the penetration of oxygen atoms into the silicon wafer. All these shortcomings complicate the production and widespread use of silicon-on-insulator structures obtained by the existing method.

The technical result of the invention is to eliminate defects such as "silicon tubes" buried insulating layer and simplify the manufacturing process.

The technical result is achieved in that in a method for producing a silicon-on-insulator structure, which includes encapsulation with a protective film and high-temperature annealing of a silicon wafer to form a working single-crystal silicon layer and a buried insulating layer of silicon dioxide, a hole-type single-crystal silicon wafer is used as a silicon wafer and before encapsulation with a protective film of silicon dioxide and high-temperature annealing, the silicon plate is first subjected to anodic etching It is dried in an electrolyte solution containing hydrogen and fluorine ions, then anodic oxidation is carried out in an aqueous electrolyte solution and dried again.

In the method, hole-type single-crystal silicon with a resistivity in the range of 0.005 ÷ 0.05 Ohm · cm is used as a silicon wafer.

In the method by anodic etching of a silicon wafer, bilayer porous silicon is formed, the upper layer of which has a porosity of 25 to 40%, and the lower layer of 70 to 90%.

In the method of anodic oxidation of a silicon wafer with a surface layer of porous silicon, a continuous layer of porous silicon oxide is formed at the interface with the monolithic part of the wafer.

In the method, the drying of a silicon wafer with porous layers is carried out in an inert atmosphere at temperatures from 180 to 400 ° C.

In the method, a polycrystalline silicon film is further deposited onto a silicon dioxide film.

In the method, an additional silicon nitride film is deposited onto silicon dioxide and polycrystalline silicon films.

In the method, an additional silicon nitride film is deposited onto the silicon dioxide film.

In the method, high-temperature annealing is carried out at temperatures from 1300 to 1370 ° C.

The invention is illustrated by the following description and the accompanying drawings.

Figure 1 shows a diagram of the structure of the silicon-on-insulator of the proposed method: position 1 is the source plate of single-crystal silicon hole type, position 2 is a silicon plate with two-layer porous silicon, position 3 is a silicon plate with layers of porous silicon and porous oxide silicon, located at the border with the monolithic part of the plate, position 4 is a silicon plate with porous layers and a protective film, position 5 is a silicon-on-insulator structure with a protective film. Elements: 1 - a plate of single-crystal silicon of a hole type, 2 - two-layer porous silicon, 3 - a monolithic part of the plate, 4 - a continuous layer of porous silicon oxide, 5 - a protective film, 6 - a working single-crystal layer of silicon, 7 - a buried insulating layer of silicon dioxide.

Figure 2 shows an electron microscopic image of a cross-section of a silicon-on-insulator structure with a protective film, position 5 in figure 1.

Figure 3 presents the electron microscopic image of the cross-section of the boundary of the working single-crystal silicon layer with a buried insulating layer of silicon dioxide structure "silicon-on-insulator", obtained at high resolution.

The use of hole-type single-crystal silicon wafers with a specific resistance of 0.005 ÷ 0.05 Ohm · cm (Fig. 1 pos. 1 element 1) allows anodic etching to obtain bilayer porous silicon with a mesoporous structure (Fig. 1 pos. 2 element 2). During high-temperature annealing, the upper layer of porous silicon is sintered into monolithic single-crystal silicon, forming a working layer of a silicon-on-insulator structure (Fig. 1, item 5, element 6). During anodic etching of silicon wafers with a specific resistance greater than 0.05 Ohm · cm, porous silicon with a microporous structure is formed, which turns into polycrystalline silicon upon annealing, which is unacceptable for silicon-on-insulator structures. The processing of silicon wafers having a resistivity of less than 0.005 Ohm · cm leads to the formation of heavily doped working single-crystal silicon layers and thereby significantly limits the application of silicon-on-insulator structures.

Obtaining porous silicon with a two-layer structure allows anodic oxidation to form at the boundary of the lower highly porous silicon layer with the monolithic part of the wafer a continuous layer of porous silicon oxide (Fig. 1, item 3 element 4), which is sintered into a monolithic dielectric upon high-temperature annealing, forming a buried insulating layer silicon dioxide structure "silicon-on-insulator" (figure 1, pos. 5 element 7). The porosity of the lower layer in the range of 70-90% avoids the anodic oxidation of the upper low-porosity silicon, which forms a working single-crystal silicon layer during high-temperature annealing (Fig. 1, item 5 element 6). When the porosity of the lower layer is less than 70%, anodic oxidation of the upper layer occurs, which complicates the formation of a working single-crystal silicon layer in its place during annealing. Layers with porosity greater than 90% are mechanically unstable and, upon subsequent anodic oxidation, destroy the structure. The porosity of the upper layer in the structure of porous silicon, claimed in the range of 25-40%, is established on the basis of the following laws. A porosity of 25% is the lower limit achieved by anodic etching of the selected silicon, and layers of porous silicon having more than 40% porosity are transformed into defective layers of crystalline monolithic silicon at high temperature annealing, which significantly degrade the properties of the silicon-on-insulator structure .

The drying of silicon wafers with porous layers in an inert medium, carried out at temperatures from 180 to 400 ° C, removes from the porous layers solutions of electrolytes and products of electrochemical reactions, which is especially necessary when changing solutions with different effects on silicon, namely, anode etching and oxidation. At temperatures below 180 ° C, drying does not provide evaporation of water from the porous layers, and upon heating above 400 ° C, undesirable oxidation of porous silicon occurs both with water molecules that have not had time to evaporate and with background oxygen in the inert medium used. Also, at temperatures above 400 ° C, the chemical reactions of porous silicon with hydrocarbons and their derivatives are accelerated, which leads to the irreversible formation of bonds of silicon and carbon atoms, which, upon high-temperature annealing, turn into precipitates of silicon carbide, an unremovable silicon-on-insulator structural defect.

During the anodic oxidation of porous silicon, a continuous layer of porous silicon oxide is created (Fig. 1, pos. 3), which, during high-temperature annealing, serves as a seed to form a buried insulating layer of silicon dioxide at the interface with the monolithic part of the plate (Fig. 1, pos. 5). The continuity of this oxide layer created by the electrochemical process is a prerequisite for the successful fabrication of a silicon-on-insulator structure.

The use of the encapsulation operation with a protective film protects the silicon wafer with porous layers of silicon and silicon oxide from the external environment and thermal evaporation during high-temperature annealing. The protective film consists of one or more layers, each of which performs a certain function depending on the environment and the required purity of the resulting silicon-on-insulator structures. The deposited silicon dioxide film prevents the thermal evaporation of the working single-crystal silicon layer and the buried insulating layer of silicon dioxide and is used for annealing in a pure inert medium. The additionally deposited polycrystalline silicon film serves as a gettering element in the annealed structure, chemically bonding background impurities present in the external environment (oxygen, metal oxides, etc.) and in the silicon wafers used (iron, copper, etc.). Additionally, the deposited film of silicon nitride is an effective diffusion barrier for penetration into the formed structure of almost all chemical elements of the environment and is used in cases where the medium is not well controlled.

During high-temperature annealing at temperatures from 1300 to 1370 ° C for 2-12 hours, porous layers of silicon and silicon oxide are sintered (Fig. 1, pos. 3 elements 2 and 3), resulting in the formation of a silicon-on-insulator structure, presented in figure 2, consisting of a working single-crystal layer of silicon and a buried insulating layer of silicon dioxide (figure 1 pos.5 and figure 2 elements 6 and 7). Annealing at temperatures less than 1300 ° C does not allow creating a layered structure with clearly separated areas of silicon and silicon dioxide; extended intermediate zones remain with inclusions of both phases. At annealing temperatures above 1370 ° C, numerous defects occur in the silicon-on-insulator structure caused by crystallization of silicon dioxide in the insulating and encapsulating layers, which leads to the destruction of the structure.

Example 1

1. Anode etching: a plate of single-crystal silicon of a hole type with a specific resistance of 0.005 Ohm · cm (Fig. 1 item 1 element 1) is treated in a 20% aqueous-alcoholic HF solution at current densities of 1 and 90 mA / cm ² for 180 and 3 seconds, respectively. In this case, bilayer porous silicon is formed (Fig. 1, pos. 2 element 2), the upper layer of which has a porosity of 25%, and the lower one - 70%.

2. Drying the silicon wafer with a porous layer is carried out in an atmosphere of an inert argon gas at a temperature of 180 ° C for 10 minutes.

3. Anodic oxidation: a silicon wafer with a porous layer is treated in a 0.12 M aqueous HCl solution at a constant current density of 0.33 mA / cm ² (Fig. 1 item 3 element 4).

4. The drying of a silicon plate with porous layers of silicon and silicon oxide is carried out in an atmosphere of an inert argon gas at a temperature of 180 ° C for 10 minutes.

5. Encapsulation of the protective film is performed by deposition of silicon dioxide (figure 1, position 4 element 5).

6. High-temperature annealing is carried out at a temperature of 1300 ° C in an atmosphere of inert argon gas for 12 hours (figure 1, position 5, elements 6 and 7).

Example 2

1. Anode etching: a plate of single-crystal silicon of a hole type with a specific resistance of 0.05 Ohm · cm (Fig. 1 item 1 element 1) is treated in an aqueous solution of NH ₄ F and HCl at current densities of 15 and 300 mA / cm ² for 180 and 3 seconds respectively. In this case, bilayer porous silicon is formed (Fig. 1, pos. 2 element 2), the upper layer of which has a porosity of 40%, and the lower one - 90%.

2. Drying the silicon wafer with a porous layer is carried out in an atmosphere of inert argon gas at a temperature of 400 ° C for 2 minutes.

3. Anodic oxidation: a silicon wafer with a porous layer is treated in a 0.12 M aqueous HCl solution at a constant current density of 0.33 mA / cm ² (Fig. 1 item 3 element 4).

4. Drying the silicon wafer with a porous layer is carried out in an atmosphere of an inert argon gas at a temperature of 400 ° C for 2 minutes.

5. The encapsulation of the protective film is carried out by sequential deposition of silicon dioxide and silicon nitride.

6. High-temperature annealing is carried out at a temperature of 1370 ° C in an atmosphere of inert argon gas for 2 hours (Fig. 1, pos. 5 elements 6 and 7).

Example 3

1. Anode etching: a plate of single-crystal silicon of a hole type with a specific resistance of 0.006 Ohm · cm (Fig. 1 item 1 element 1) is treated in a 20% aqueous-alcoholic solution of HF at current densities of 3 and 240 mA / cm ² for 180 and 3 seconds respectively. In this case, bilayer porous silicon is formed (Fig. 1, item 2 element 2), the upper layer of which has a porosity of 33%, and the lower one - 85%.

2. Drying the silicon wafer with a porous layer is carried out in an atmosphere of inert argon gas at a temperature of 300 ° C for 5 minutes.

3. Anodic oxidation: a silicon wafer with a porous layer is treated in a 0.12 M aqueous HCl solution at a constant current density of 0.33 mA / cm ² (Fig. 1 item 3 element 4).

4. Drying the silicon wafer with a porous layer is carried out in an atmosphere of inert argon gas at a temperature of 300 ° C for 5 minutes.

5. The encapsulation of the protective film is carried out by sequential deposition of silicon dioxide, polycrystalline silicon and silicon nitride.

6. High-temperature annealing is carried out at a temperature of 1340 ° C in an inert atmosphere of argon for 8 hours.

The structure of the silicon-on-insulator "made by the proposed method, have the following typical characteristics:

the thickness of the buried insulating layer of silicon dioxide ~ 0.2 μm,

the thickness of the working single-crystal silicon layer is ~ 0.2 μm,

average dielectric breakdown voltage ~ 130 V,

dielectric breakdown field strength ~ 6.4 · 10 ⁶ V / cm,

absence in the buried insulating layer of defects such as "silicon tubes",

the absence in the working layer of silicon of defects such as a dislocation, stacking faults, and foreign phase inclusions.

The obtained parameters indicate the high quality of the structures "silicon-on-insulator" made by the proposed method.

The use of the proposed method for obtaining structures of "silicon-on-insulator" provides, compared with existing methods, the following advantages:

reduction of production costs for the manufacture of silicon-on-insulator structures and devices based on them due to the use of simple technological equipment of traditional silicon rulers, which does not require highly qualified service and special labor protection measures required when operating high-voltage and radiation hazardous installations;

an increase in the output of electronic equipment products due to the extensive development of production on the basis of simple technological equipment and mass processing of structures;

expanding the range of electronic products due to the affordable production of sensors and devices of nano- and microelectromechanical systems.

Claims (9)

1. A method of producing a silicon-on-insulator structure, comprising encapsulating a silicon dioxide protective film and high-temperature annealing of a silicon wafer to form a working single-crystal silicon layer and a buried insulating silicon dioxide layer, characterized in that a single-walled silicon single-walled silicon plate is used type, and before encapsulation with a protective film of silicon dioxide and high-temperature annealing, the silicon plate is first subjected to anodic etching electrolyte solution containing hydrogen ions and fluorine, dried and then subjected to anodic oxidation in an aqueous electrolyte solution and dried again. 2. The method according to claim 1, characterized in that hole-type single-crystal silicon with a specific resistance in the range of 0.005-0.05 Ohm · cm is used as a silicon wafer. 3. The method according to claim 1, characterized in that anodic etching of the silicon wafer forms a two-layer porous silicon, the upper layer of which has a porosity of 25 to 40%, and the lower one - from 70 to 90%. 4. The method according to claim 1, characterized in that by anodic oxidation of the silicon wafer with a surface layer of porous silicon, a continuous layer of porous silicon oxide is formed at the interface with the monolithic part of the plate. 5. The method according to claim 1, characterized in that the drying of the silicon plate with porous layers is carried out in an inert medium at temperatures from 180 to 400 ° C. 6. The method according to claim 1, characterized in that an additional film of polycrystalline silicon is deposited on the silicon dioxide film. 7. The method according to claim 6, characterized in that the film of silicon dioxide and polycrystalline silicon additionally deposit a film of silicon nitride. 8. The method according to claim 1, characterized in that the silicon nitride film is additionally deposited on the silicon dioxide film. 9. The method according to claim 1, characterized in that the high-temperature annealing is carried out at temperatures from 1300 to 1370 ° C.

Images